The Senses Sensory Receptors on sensory neurons Sensation perception that occurs when brain interprets sensory impulse. Primary Receptor Types Chemoreceptors respond to changes in chemical concentrations Pain receptors respond to tissue damage Thermoreceptors respond to changes in temperature Mechanoreceptors respond to movement Photoreceptors respond to light Sensory Adaptation adjustment of sensory receptors from continuous stimulation stronger stimulus required to activate receptors Pain receptors do not undergo adaptation at the receptor site. Touch and Pressure Senses Free nerve endings common in epithelial tissues detect touch and pressure Meissners corpuscles abundant in hairless portions of skin detect light touch Pacinian corpuscles common in deeper subcutaneous tissues, tendons, and ligaments detect heavy pressure Touch and Pressure Senses Temperature Senses Warm receptors sensitive to temperatures above 25 o C (77 o F) unresponsive to temperature above 45 o C (113 o F) Cold receptors sensitive to temperature between 10 o C (50 o F) and 20 o C (68 o F) Pain receptors respond to temperatures below 10 o C respond to temperatures above 45 o C Sense of Pain free nerve endings widely distributed nervous tissue of brain lacks pain receptors stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature do not adapt Visceral Pain may exhibit referred pain not well localized Referred Pain may occur due to sensory impulses from two regions following a common nerve pathway to brain Regulation of Pain Impulses Thalamus allows person to be aware of pain Cerebral Cortex judges intensity of pain locates source of pain motor response to pain emotional response to pain Pain Inhibiting Substances enkephalins serotonin endorphins Stretch Receptors proprioceptors send information to CNS concerning lengths and tensions of muscle fibers Smell - Olfaction Olfactory Receptors chemoreceptors respond to chemicals dissolved in liquids Olfactory Organs contain olfactory receptors and supporting epithelial cells cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum Interpreted in the temporal lobe of the cerebral cortex Adaptation occurs after 1-5 min. of continuous stimulation. Olfactory Receptors Taste (Gustation) another chemical sense. Taste Buds organs of taste located around papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx Taste Sensations Four Primary Taste Sensations sweet stimulated by carbohydrates sour stimulated by acids salty stimulated by salts bitter stimulated by many organic compounds Spicy foods activate pain receptors Taste Nerve Pathways Sensory impulses from taste receptors travel along cranial nerves (facial, vagus, glossopharyngeal) to medulla oblongata to thalamus to gustatory cortex in parietal lobe (for interpretation) Hearing Ear organ of hearing 3 Sections External Middle Inner External Ear Auricle External auditory meatus Tympanic membrane Middle Ear tympanic cavity auditory ossicles malleus, incus, stapes oval window Auditory Tube eustachian tube Inner Ear Organ of Corti (inside cochlea) Auditory Nerve Pathways Semicircular Canals three canals at right angles rapid turns of head or body stimulate hair cells by shifting gel inside the canals. Sight Visual Accessory Organs eyelids lacrimal apparatus extrinsic eye muscles Eyelid conjunctiva mucous membrane; lines eyelid and covers portion of eyeball Eyelashes and eyebrows help filter sun/debris Lacrimal Apparatus lacrimal gland lateral to eye secretes tears, drain into lacrimal puncta, drains into nasal cavity. Tears contain lysozyme Structures of the eye Lens Ciliary Body forms internal ring around front of eye ciliary processes radiating folds ciliary muscles contract and relax to move lens Accommodation changing of lens shape to view objects Iris Light Refraction Refraction bending of light occurs when light waves pass at an oblique angle into mediums of different densities Types of Lenses Convex lenses cause light waves to converge Concave lenses cause light waves to diverge Focusing On Retina as light enters eye, it is refracted by convex surface of cornea convex surface of lens image focused on retina is upside down and reversed from left to right Visual Receptors Rods rhodopsin hundred times more sensitive to light than cones not sensitive to color Cones red, green, and blue provide vision in bright light produce sharp images produce color vision Visual Pathway